In general, a color photographic material comprises color sensitive emulsion layer units having color sensitivity different from one another which are provided on a support, the units each containing at least one silver halide emulsion layer. (The color sensitivity herein means a nature to have sensitivity to any one of three regions of visible spectrum, that is, red, green and blue.
In the field of color photographic materials, and particularly, in the color reversal photographic materials which are frequently used by professional photographers, high-sensitivity color photographic materials are required to take sports photographs which need high shutter speed or to shoot particular scenes under insufficient quantity of light for exposure like stage photography. However, the high-sensitivity color photographic materials have coarse granularity, and therefore, improvement in the relation between sensitivity and granularity has been desired.
On the other hand, sensitivity adjustment owing to processing has also been conducted to compensate for underexposure. This sensitivity adjustment owing to processing is usually called "push-processing", and in the color reversal photographic materials, push-processing is done by extending the standard processing time in the first development (black-and-white development).
However, conventional color reversal photographic materials do not necessarily have sufficient push-processing suitability. In fact, the first development requires time much longer than the standard processing time to obtain high sensitivity in some cases, or in some photographic materials having a structure composed of two layers, a high sensitivity layer and a low sensitivity layer, different push-processing suitability of both the layers causes variation in gradation owing to the push-processing. An attempt to increase an extent of the push-processing by extending the first development time often results in a marked decrease in color image densities, or difference in the push-processing suitability among a red sensitive layer, a green sensitive layer and a blue sensitive layer causes deterioration in color balance in some cases.
Accordingly, the development of techniques for bringing about an excellent relationship between the sensitivity and the granularity and for obviating defects caused by the push-processing has been desired.
JP-A-51-128528 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") (U.S. Pat. No. 4,082,553) discloses that a color reversal photographic material having silver halide emulsion layers which are studded with silver halide grains fogged at the surfaces thereof is improved in the interlayer effect. However, the surface-fogged silver halide grains should be differentiated from silver halide grains fogged in the interior thereof (claim (11) in JP-A-51-128528), and addition of such surface-fogged silver halide grains has an adverse effect on photographic properties in standard processing, and in addition, the disadvantage of markedly lowering densities of color images owing to the push-processing.
U.S. Pat. Nos. 2,996,382, 3,178,282 and 3,397,987 disclose that incorporation of both silver halide grains capable of forming surface latent images on exposure and silver halide grains containing internal fog nuclei into emulsion layers raises the sensitivity and the contrast of a negative image forming photographic element. However, these specifications give no description of push-processing, or conventional color reversal photographic materials at all. Further, in this photographic element, the silver halide grains having the surface latent images release a reaction product in response to exposure amounts during development after exposure, the reaction product generating cracks in the silver halide grains containing internal fog nuclei to make development possible. Therefore, this causes the sensitivity and the contrast to increase even in standard processing to make it impossible to control the sensitivity raised owing to the push-processing.
Further, it is described in JP-B-46-19024 (The term "JP-B" as used herein means an "examined Japanese patent publication") (U.S. Pat. No. 3,505,068) that, with a color reversal photographic material in which a color sensitive emulsion layer is composed of a high sensitivity layer and a low sensitivity layer, the contrast can be efficiently lowered, when silver iodide is used for the high sensitivity layer and grains in which cores consisting of silver haloiodide are covered with shells composed of a silver halide which contains no silver iodide at all are used for the low sensitivity layer. However, the core-shell type silver halide grains used herein exhibit no particular action on the push-processing, because they contain no fog nuclei in the interior thereof.
Further, JP-A-59-214852 discloses that, as a technique for yielding no variation in gradation and no deterioration in color balance and for controlling relatively small the extent of decrease in the densities of color images due to the push-processing, a silver halide emulsion containing fog nuclei in the interior thereof is incorporated into silver halide emulsion layers or layers adjacent to the silver halide emulsion layers, and these fog nuclei function in the push-processing to promote development. In this technique, the sensitivity of the emulsion layers into which a silver halide emulsion having fog nuclei in the interior thereof is incorporated increases on push-processing, and therefore the addition of this emulsion to the emulsion layers undergoing relatively limited extent of sensitization makes it possible to adjust color balance after the push-processing. However, when the sensitivity increase of a particular emulsion layer after the push-processing is extremely large, even incorporation of a large amount of the above-mentioned silver halide emulsion having fog nuclei in the interior thereof into the emulsion layers undergoing a limited extent of sensitization brings about insufficient sensitivity increase in some cases. In these cases, the push-processing gives no satisfactory color balance, and in addition, the incorporation of a large amount of the emulsion having fog nuclei in the interior thereof results in decrease in densities of color images.
On the other hand, colloidal silver is known to improve developing activity of the neighborhood more than the above-mentioned fogged emulsion. Photographic materials containing colloidal silver in emulsion layers or adjacent layers thereof are described, for example, in JP-A-60-126652, JP-A-63-304252, JP-A-2-110539, JP-A-3-113438, JP-A-3-226732, and U.S. Pat. No. 979,001. Of these patents, U.S. Pat. No. 979,001, JP-A-60-126652, JP-A-63-304252, JP-A-2-110539, and JP-A-3-113438 aim at improving image quality and gradation reproduction. Although JP-A-3-226732 refers to the push-processing suitability, it does not state at all that yellow colloidal silver gives high push-processing suitability, and an attempt to incorporate yellow colloidal silver into each layer adjacent to the color sensitive layers is not made. To put it shortly, the effect of colloidal silver on improvement in developing activity, that is, what colloidal silver should be used or how the colloidal silver should be incorporated into a photographic material, has never been examined in order to improve the push-processing suitability.
The process for preparing the tabular silver halide grains and the technique for using them are already disclosed, for example, in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353, JP-A-59-994335, JP-A-60-209445, and JP-A-63-151618. Some advantages are known about it, which include sensitivity increase including improvement in efficiency of color sensitization due to sensitizing dyes, good relationship between the sensitivity and the granularity, improvement in sharpness due to peculiar, optical nature of the tabular grains and improvement in covering power.
JP-A-59-133540 discloses a silver halide emulsion containing silver halide host grains which are mainly enclosed with {111} crystal faces and have an average aspect ratio smaller than 8:1 and a silver salt which is epitaxially located on selected surface sites of the host grains and substantially limited to the sites, in which the silver halide host grains contain the iodide in an amount insufficient for the epitaxial silver salt to be directed to the selected surface sites of the host grains. However, this specification gives no description of the push-processing which this silver halide emulsion may undergo.
It is mentioned in JP-A-63-244030 (corresponding to U.S. Pat. No. 4,888,272) that a photographic material in which silver halide grain substrates have projections on the surfaces thereof and the projections have silver halide composition different from that of the substrates so that the solubility of the projections in developing solution can be higher than the solubility of the substrates in developing solution provides enhanced sharpness without sensitivity decrease. It is revealed, however, that the flexibility to control of the push-processing is insufficient, because the solubility of the projections is much greater than that of the substrates so that the projections dissolve in processing solution in a short period of time.